Method of machining metallic tubes

ABSTRACT

A method of machining a tube includes performing an obverse drawing process to the tube, where the obverse drawing process draws the tube in an obverse drawing direction from a first end toward a second end of the tube. The tube is turned around to perform a reverse drawing process, where the reverse drawing process draws the tube in a reverse drawing direction from the second end toward the first end of the tube. The obverse and the reverse drawing processes are alternately performed until the tube is thinned to a desired thickness.

RELATED APPLICATIONS

The application claims priority to Taiwan Application Serial Number 96132107, filed Aug. 29, 2007, which is herein incorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to method of machining tubes. More particularly, the present invention relates to a method of machining metallic tubes, which improves mechanical strength of the processed metallic tubes while the weight of the processed metallic tubes is reduced.

2. Description of Related Art

Metallic tubes have extensive applications in various industrial products and fields. Fabricating mechanically strong, light tubes are long-term objectives for skilled people in this art. Thus, various approaches including improved machining methods and metallic materials (such as alloy) have been continuously developed and suggested.

Severe plastic deformation (SPD) is a processing method to improve the mechanical strength of metallic materials. SPD refines the grain structure (such as the grain size) of the metallic material to produce lots of dislocations in the grain structure of the material by means of producing severe plastic deformations to the material. The produced dislocations can enhance the mechanical strength of the material. Thus, using less metallic material processed by SPD can provide the same mechanical strength, which results in lowering the entire weight of the material used. However, SPD such as equal channel angular pressing (ECAP) is only suitable for processing solid cylinders or bars. SPD cannot be not used to process tubes.

Refer to FIG. 1 a and FIG. 1 b. Based on the principles of the SPD, a tube is typically machined or processed by drawing technology that produces the dislocations in the tube to enhance the mechanical strength of the tube. For example, a tube 100 is processed with an anneal treatment before a drawing process to soften it. A pressing portion 120 is formed at a first end 110 of the annealed tube 100 as shown in FIG. 1 a. A plug 200 is inserted into the tube 100 through a second end 130 of the tube 100 until the plug abuts against the pressing portion 120 as shown in FIG. 1 b.

The tube 100 is pushed into an eye hole 220 of a die 210 by the plug 200 through the pressing portion 120. When the tube 100 passes through the eye hole 210, the eye hole 220 restricts the external diameter of the tube 100, which reduces the thickness of the tube 100 to produce lots of plastic deformations to the tube 100. Then, the tube 100 is drawn out of the eye hole 220 from its second end 130 after the entire tube 100 passes completely through the eye hole 220.

The aforementioned process is repeated. The plug 200 pushes the tube 100 into another eye hole with a smaller diameter by the pressing portion 120, and then the tube 100 is drawn out of the eye hole from its second end. The tube 100 is repeatedly drawn until the thickness of the tube 100 meets a desired thickness.

Refer to FIG. 2 a to FIG. 2 c. The conventional method of drawing the tubes utilizes the plug 200 to repeatedly push the tube 100 into the various eye holes with different diameters through the tube's first end 110. That means the tube 100 is drawn in a single drawing direction (DD), i.e. the direction from the first end 120 towards the second end 130. This prior art method only can produce few dislocations 142 in regions neighboring the slip planes 141 located along a common orientation between the grains 140. Both the amount of dislocations 142 and effects of the dislocations 142 are restricted and not sufficient. Thus, the mechanical strength of the tube cannot be efficiently improved or enhanced.

Therefore, there is a need to provide an improved method of machining a metallic tube to mitigate or obviate the aforementioned problems.

SUMMARY

An object of the present invention is to provide a method of machining a metallic tube so that the mechanical strength of the metallic tube is improved, the thickness of the metallic tube is reduced and the weight of the metallic tube is lowered.

An embodiment of a method of machining a metallic tube includes performing an obverse drawing process to the tube, where the obverse drawing process draws the tube in a drawing direction from a first end toward a second end of the tube. The tube is turned around to perform a reverse drawing process, where the reverse drawing process draws the tube in a drawing direction from the second end toward the first end of the tube. The aforementioned processes are alternately performed until the tube is thinned to a desired thickness.

Another embodiment of a method of machining a metallic tube having a first end and a second end passes the metallic tube through a first eye hole from the first end. The metallic tube is drawn out the metallic tube from the first eye hole where the first eye hole has a diameter smaller than the external diameter of the metallic tube. Then, the method passes the metallic tube through a second eye hole from the second end and draws out the metallic tube from the second eye hole where the second eye hole has a diameter smaller than the external diameter of the metallic tube. The metallic tube is alternately and repeatedly drawn until the tube is thinned to a desired thickness.

Another embodiment of a method of machining a metallic tube having a first end and a second end forms a first pressing portion at the first end. The method inserts a first plug into the metallic tube from the second end until the first plug abuts against the first pressing portion, and draws the metallic tube out of an eye hole after the first plug pushes the metallic tube passing through the eye hole where the first plug has the external diameter larger than the internal diameter of the metallic tube. The first pressing portion is removed, and a second pressing portion is formed at the second end.

Likewise, the method inserts a second plug into the metallic tube from the first end until the second plug abuts against the second pressing portion, and draws the metallic tube out of the eye hole after the second plug pushes the metallic tube passing through the eye hole where the second plug has an external diameter larger than the internal diameter of the metallic tube. The second pressing portion is removed. The metallic tube is repeatedly and alternatively drawn until the metallic tube meets a predetermined thickness.

The tube is repeatedly and alternatively drawn from the first end and the second end with the dies and the plugs, i.e. the tube is drawn in both drawing directions (an obverse drawing direction and a reverse drawing direction). Hence, the dislocations are produced in the regions neighboring the slip planes such as a first slip plane and a second slip plane that are arranged in different orientations between the grains of the tube. Lots of dislocations are produced in the tube, which enhances and improves the mechanical strength of the tube, reduces the thickness of the tube and simultaneously lowers the weight of the tube.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:

FIG. 1 a is a schematic section view of a tube being drawn with a die and a plug;

FIG. 1 b is a schematic section view of the tube in FIG. 1 a before machining;

FIG. 2 a to FIG. 2 c are schematic views showing changes to grain structures of the tube before and after tube drawing in accordance with the prior art;

FIG. 3 a to FIG. 3 c are schematic views showing an obverse drawing process of an embodiment of a method in accordance with the present invention;

FIG. 4 a to FIG. 4 c are schematic views showing a reverse drawing process following the obverse drawing process of the embodiment shown in FIG. 3 a to FIG. 3 c;

FIG. 5 a to FIG. 5 c are schematic views showing a repeated obverse drawing process following the reverse drawing process of the embodiment shown in FIG. 4 a to FIG. 4 c;

FIG. 6 a to FIG. 6 c are schematic views showing changes to grain structures of the tube before and after tube drawing process in accordance with the present invention;

FIG. 7 a is a section view of a second embodiment of the tube; and

FIG. 7 b is a section view of a third embodiment of the tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

An embodiment of a method of machining a metallic tube draws the tube with the eye hole of the die by passing the tube through the eye hole from the tube's the second end. After the tube is drawn out of the eye hole, the tube is turned around, and the tube is drawn through the eye hole from the tube's first end. The aforementioned steps are repeated until the thickness of the tube meets a predetermined thickness. The tubes may be circular tubes, rectangular tubes, angular tubes, etc. and are metallic tubes.

Refer to FIG. 3 a to FIG. 3 c. In an embodiment of the present invention, the method reduces the external diameter of a tube 300, and the internal diameter of the tube 300 is unchanged. Thus, the thickness of the tube 300 is reduced to simultaneously lower the weight of and enhance the mechanical strength of the tube 300 after the tube 300 is processed.

After the annealing treatment is performed on the tube 300, a first pressing portion 311 is formed at a first end 310 of the tube 300. The first pressing portion 311 is formed by necking the first end 310 of the tube 300. The tube 300 is treated with a soap treatment that coats a layer of lubricant, such as a solid soap substance on surfaces of the tube 300.

A plug 700 is inserted into the tube 300 from its second end 320 and abuts against the pressing portion 311, which enables the plug 700 to push the tube 300 through an eye hole 410 of a die 400 (a first die) from the tube's first end 310. The plug 700 may be driven by hydraulic power. After the tube 300 passes completely through the eye hole 410, the tube 300 is drawn out of the eye hole 410. The first pressing portion 311 is cut off or removed as shown in FIG. 3 c. Since the diameter of the eye hole 410 is smaller than the external diameter of the tube 300, the external diameter of the tube 300 becomes the diameter of the eye hole 410 after the plug 700 pushes the tube 300 through the eye hole 410.

Refer to FIG. 4 a to FIG. 4 c. A second pressing portion 321 is formed at the second end 320 of the tube 300 by necking the second end 320 as shown in FIG. 4 a.

Likewise, the plug 700 is inserted into the tube 300 from the first end 310 and abuts against the second pressing portion 321. The plug 700 may be driven by hydraulic power, and pushes the tube 300 through an eye hole 510 of a die 500 (a second die) from the second end 320 of the tube 300 to further reduce the external diameter of the tube 300. After the tube 300 passes completely through the eye hole 510, the tube is drawn out of the eye hole 510. The second pressing portion 321 is cut off or removed as shown in shown in shown in FIG. 4 c.

Refer to FIG. 5 a and FIG. 5 c. The aforementioned processes are repeated. A third pressing portion 313 is formed at the first end 310 of the tube 300 by necking the first end 310 as shown in FIG. 5 a. The plug 700 is inserted into the tube 300 from the second end 320 and abuts against the third pressing portion 313. The plug 700 may be driven by hydraulic power to push the tube 300 through an eye hole 610 of a die 600 (a third die) from the first end 310. After the tube 300 passes completely through the eye hole 610, the tube 300 is drawn out. The third pressing portion 313 is cut off or removed as shown in FIG. 5 c. The tube 300 is repeatedly and alternatively drawn from the first end 310 and the second end 320 until the thickness of the tube 300 meets a predetermined thickness.

Refer to FIG. 6 a to FIG. 6 c. An embodiment of a method of drawing a tube in accordance with the present invention, the tube 300 is repeatedly and alternatively drawn from the first end 310 and the second end 320 with the dies, i.e. the tube 300 is drawn in both drawing directions of the tube 300 (an obverse drawing direction and a reverse drawing direction). Hence, many dislocations 333 are produced in the regions neighboring the slip planes such as a first slip plane 331 and a second slip plane 332 that are arranged in different orientations between the grains 330 of the tube 300. Thus, lots of dislocations 333 are produced in the tube 300, which enhances and improves the mechanical strength of the tube 300 and reduces simultaneously the weight of the tube 300.

Refer to FIG. 7 a to FIG. 7 b. The tube 300 may be a circular metallic tube as previously illustrated. The method in accordance with the present invention may be also applied to rectangular metallic tube, non-circular metallic tube, hexangular metallic tubes, or the like.

Embodiment 1

For machining a 7050 Al—Zn—Mg aluminum tube as an example, before machining the tube, the original external diameter of the tube is 31 millimeters, the original internal diameter of the tube is 25 millimeters, the thickness of the tube is 3 millimeters, and the length of the tube is 250 millimeters. A predetermined thickness of the tube is 1.5 millimeters after machining. This embodiment illustrates reducing the external diameter of the tube from 31 millimeters to 28 millimeters, while the internal diameter of the tube is still kept at 25 millimeters after machining.

The tube is annealed at 430° C. for one hour, and furnace cooled. The annealing treatment softens the tube. A portion (about 25 millimeters in length) of the tube at the first end is necked to form the first pressing portion. A soap treatment is performed to the surface of the tube, which coats a layer of solid soap material on the surface of the tube. The soap treatment may immerse the tube in sulfurized oil, chlorination paraffin etc. so that a layer of solid soap material is coated on the surface of the tube to lubricate during drawing process.

The drawing process uses equipments including a drawing tube machine (75 horsepower), two sets of die including a first set of die and a second set of die, and a plug. The first set of die has an eye hole with a diameter of 29 millimeters, and the second set of die has an eye hole with a diameter of 28 millimeters. The plug has an external diameter of 25 millimeters and a length of 1 meter.

The plug is driven by hydraulic power and pushes the tube forward at a speed of 5 meters per minute. Thus, an obverse drawing direction of the first drawing process to the tube is from the second end toward the first end of the tube. That means the plug enters the tube from its second end, moves toward the first end and abuts against the first pressing portion. When the plug pushes the tube passing through the eye hole (with the diameter of 29 millimeters) of the first set of die, the tube is drawn along the obverse drawing direction because the diameter of the eye hole is smaller than the external diameter of the tube (31 millimeters) and the diameter of the plug is equal to the internal diameter of the tube. The first drawing process to the tube is complete after the entire tube has passed through the eye hole of the first set of die. The first drawing process reduces the external diameter of the tube from 31 millimeters to 29 millimeters without changing the internal diameter of the tube. Thus, the tube is elongated and thinned by drawing. Then, a second drawing process is performed.

The first pressing portion is removed or cut off, and a second pressing portion is formed at the second end of the tube before the second drawing process. The second drawing process draws the tube in a reverse drawing direction that is opposite to the obverse drawing direction. The reverse drawing direction means from the first end toward the second end of the tube. Meanwhile, the second drawing process uses the second set of die that has the eye hole with a diameter of 28 millimeters. The plug is still 1 meter in length and its diameter is 25 millimeters.

Likewise, the plug is driven by hydraulic power and pushes the tube forward at a speed of 5 meters per minute. The plug enters the tube from its first end, moves toward the second end and abuts against the second pressing portion. When the plug pushes the tube passing through the eye hole (with the diameter of 28 millimeters) of the second set of die, the tube is drawn along the reverse direction because the diameter of the eye hole is smaller than the external diameter of the tube (29 millimeters) and the diameter of the plug is equal to the internal diameter of the tube. The second drawing process to the tube is complete after the entire tube has passed through the eye hole of the second set of die. The second drawing process further reduces the external diameter of the tube from 29 millimeters to 28 millimeters without changing the internal diameter of the tube. Thus, the tube is elongated and thinned by drawing again. The thickness of the tube is thinned to be 1.5 millimeters.

Embodiment 2

For machining a 7050 Al—Zn—Mg aluminum tube as an example, before machining the tube, the original external diameter of the tube is 31 millimeters, the original internal diameter of the tube is 25 millimeters, the thickness of the tube is 3 millimeters, and the length of the tube is 250 millimeters. A predetermined thickness of the tube is 1.5 millimeters after machining. This embodiment illustrates increasing the internal diameter of the tube from 25 millimeters to 28 millimeters, while the external diameter of the tube is still kept at 31 millimeters after machining.

The tube is annealed at 430° C. for one hour, and furnace cooled. The annealing treatment softens the tube. A portion (about 25 millimeters in length) of the tube at the first end is necked to form the first pressing portion.

A soap treatment is performed to the surfaces including an exterior surface and an interior surface of the tube, which coats a layer of soap material on each surface of the tube. The soap treatment may immerse the tube in sulfurized oil, chlorination paraffin etc. so that a layer of solid soap material is coated on each surface of the tube to lubricate during drawing process.

The drawing process uses equipments including a drawing tube machine (75 horsepower), a set of die, and three plugs including a first plug, a second plug and a third plug. The set of die has an eye hole with a diameter of 31 millimeters equal to the external diameter of the tube. The first plug has an external diameter of 26 millimeters. The second plug has an external diameter of 27 millimeters. The third plug has an external diameter of 28 millimeters. Each of the plugs has a length of 1 meter and a tapered front.

The first plug (with an external diameter of 26 millimeters) is driven by hydraulic power and pushes the tube forward at a speed of 5 meters per minute. Thus, an obverse direction of the first drawing process to the tube is from the second end toward the first end of the tube. That means the first plug enters the tube from its second end and moves toward the first end. Since the internal diameter of the tube (25 millimeters) is smaller than the external diameter of the first plug (26 millimeters), and the first plug has a tapered front, the first end of the tube is abutted against a blocking object when the first plug begins to enter the second end of the tube. The first plug is coercively squeezed into the tube and moved in the obverse direction until the first plug abuts against the first pressing portion. The external diameter of the tube is enlarged by the insertion of the first plug.

The blocking object is removed when the first plug has abutted against the first pressing portion. When, the first plug pushes the tube passing through the eye hole (with the diameter of 31 millimeters) of the set of die, the tube is drawn along the obverse drawing direction because the diameter of the eye hole (31 millimeters) is smaller than the external diameter of the tube (more than 31 millimeters). The first drawing process to the tube is complete after the entire tube has passed through the eye hole of the set of die. The first drawing process increases the internal diameter of the tube from 25 millimeters to 26 millimeters without changing the external diameter of the tube. Thus, the tube is elongated and thinned by drawing. Then, a second drawing process is performed.

The first pressing portion is removed or cut off, and a second pressing portion is formed at the second end of the tube before the second drawing process. The second drawing process draws the tube in a reverse drawing direction that is opposite to the obverse drawing direction. The reverse drawing direction means from the first end toward the second end of the tube. Meanwhile, the second drawing process uses the second plug that has an external diameter of 27 millimeters.

Likewise, the second plug is driven by hydraulic power and pushes the tube forward at a speed of 5 meters per minute. The second plug coercively enters the tube from its first end, moves toward the second end and abuts against the second pressing portion. When the second plug pushes the tube passing through the eye hole (with the diameter of 31 millimeters) of the set of die, the tube is drawn along the reverse drawing direction because the diameter of the eye hole is smaller than the external diameter of the tube (more than 31 millimeters). The second drawing process to the tube is complete after the entire tube has passed through the eye hole of the set of die. The second drawing process further increases the internal diameter of the tube from 26 millimeters to 27 millimeters without changing the external diameter of the tube. Thus, the tube is elongated and thinned by the second drawing process.

The tube is annealed before performing the third drawing process. The annealing process may be under conditions of 200° C., one and a half hours, and cooled by the air. Both the exterior and the interior surfaces of the tube are coated with the soap substances again as previously described.

The second pressing portion is cut off or removed. A new first pressing portion is formed at the first end of the tube by necking the first end. The third drawing process draws the tube in the obverse drawing direction, i.e. from the second end toward the first end of the tube. The third plug pushes the tube passing through the eye hole, which draws the tube because the external diameter of the third plug (28 millimeters) is larger than the internal diameter of the tube (27 millimeters). The third drawing process is complete after the second end of the tube has passed through the eye hole. The third drawing process further increases the internal diameter of the tube from 27 millimeters to 28 millimeters without changing the external diameter of the tube. Thus, the tube is elongated and thinned by the third drawing process, and the thickness of the tube becomes 1.5 millimeters.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents. 

1. A method of machining a tube, and the method comprising: a) providing a metallic tube having a first end and a second end; b) performing an obverse drawing process for the metallic tube, where the obverse drawing process draws the metallic tube in an obverse drawing direction from the first end toward the second end; c) performing a reverse drawing process for the metallic tube, where the reverse drawing process draws the metallic tube in a reverse drawing direction from the second end toward the first end; and d) repeating step b) to step c) until the metallic tube has a predetermined thickness.
 2. The method as claimed in claim 1, further comprising: annealing the metallic tube before step b) or step c).
 3. The method as claimed in claim 1, further comprising: coating a layer of lubricant on a surface of the metallic tube before step b) or step c).
 4. The method as claimed in claim 3, wherein the layer of lubricant is a solid soap substance.
 5. The method as claimed in claim 1, wherein the metallic tube is a circular tube.
 6. The method as claimed in claim 1, wherein the metallic tube is an angular tube.
 7. The method as claimed in claim 1, wherein the metallic tube is an Al—Zn—Mg tube.
 8. A method of machining a tube, and the method comprising: a) providing a metallic tube having a first end and a second end; b) passing the metallic tube through a first eye hole from the first end, and drawing out the metallic tube from the first eye hole where the first eye hole has a diameter smaller than an external diameter of the metallic tube; c) passing the metallic tube through a second eye hole from the second end, and drawing out the metallic tube from the second eye hole where the second eye hole has a diameter smaller than an external diameter of the metallic tube; and d) repeating step b) to step c) until the metallic tube meet a predetermined thickness.
 9. The method as claimed in claim 8, further comprising: annealing the metallic tube before step b) or step c).
 10. The method as claimed in claim 8, further comprising: coating a layer of lubricant on an exterior surface of the metallic tube before step b) or step c).
 11. The method as claimed in claim 10, wherein the layer of lubricant is a solid soap substance.
 12. The method as claimed in claim 8, wherein the metallic tube is a circular tube.
 13. The method as claimed in claim 8, wherein the metallic tube is an angular tube.
 14. A method of machining a tube, and the method comprising: a) providing a metallic tube having a first end and a second end; b) forming a first pressing portion at the first end; c) inserting a first plug into the metallic tube from the second end until the first plug abuts against the first pressing portion, and drawing the metallic tube out of an eye hole after the first plug pushes the metallic tube passing through the eye hole where the first plug has an external diameter larger than an internal diameter of the metallic tube; d) removing the first pressing portion; e) forming a second pressing portion at the second end; f) inserting a second plug into the metallic tube from the first end until the second plug abuts against the second pressing portion, and drawing the metallic tube out of the eye hole after the second plug pushes the metallic tube passing through the eye hole where the second plug has an external diameter larger than the internal diameter of the metallic tube; g) removing the second pressing portion; and h) repeating step b) to step g) until the metallic tube meet a predetermined thickness.
 15. The method as claimed in claim 14, further comprising: annealing the metallic tube before step c) or step f).
 16. The method as claimed in claim 14, further comprising: coating a layer of lubricant on an interior surface of the metallic tube before step c) or step f).
 17. The method as claimed in claim 16, wherein the layer of lubricant is a solid soap substance.
 18. The method as claimed in claim 14, wherein the eye hole has a diameter equal to an external diameter of the metallic tube.
 19. The method as claimed in claim 14, wherein the metallic tube is a circular tube.
 20. The method as claimed in claim 14, wherein the metallic tube is an angular tube. 